Chemical Kinetics
Rate of Reaction Average Rate Average Rate = - ∆A/∆t = ∆B/∆t Instantaneous Rate Instantaneous Rate = - dA/dt = dB/dt For every 10 K rise in temperature , instantaneous rate increases by 2 - 3 times . Temperature co-efficiebt of rate lies between 2 and 3 . Rate is directly proportional to concentration and pressure . Rate Law aA ----> bB Rate = kAxBy k is independent of initial concentration of reactants , but depends upon the temperature and type of reaction . Unit of Reaction for nth order reaction= (mol)1-n (dm3)n-1 s-1 Order of Reaction The x y in the above example is called as partial order of reaction . x + y is the overall order of reaction . Integrated Rate Laws The equations which are obtained by integrating the differential rate laws and which give a simple relationship between concentration , time and rate constant , are called as Integrated rate laws . k = (2.303/t)( log10A0/At) Half life of a reaction is the time taken for the concentration of reactants to become half the original value . t1/2 = 0.693 / k After every half life period , the concentration becomes half . Graphical Representation of First Order Reactions The integrated rate laws can be represented in the slope intercept form . y = mx + c . 1) Rate v/s Concentration Rate = kAt y = Rate , x = At Slope = k ; y-intercept = 0 2) Concentration v/s time 3) log10(At) v/s time log10At = - kt / (2.303) + log10A0 y = log10At ; x= time Slope = - k / 2.303 ; y-intercept = log10Ao 4) log10(Ao/At) v/s time kt /2.303 = ( log10A0/At) y = log10(Ao/At) ; x = time Slope = k / 2.303 ; y-intercept = 0 Zero Order Reactions Zero Order reactions are those reactions , whose rate does not depend on the concentration of reactants . Pseudo First Order Reaction Pseudo First Order Reactions are those reactions which do not have the order of 1 , but behave like first order reactions . Molecularity Molecularity of a reaction is the number of molecules participating in a reaction . It can also be the number of reactant molecules . Reaction Intermediate & Catalyst The reaction intermediate is formed in the first step and consumed in the second step . The reaction intermediate is consumed in the first step and formed in the second step . A catalyst increases the rate of reaction and can be recovered back unchanged after the completion of reaction . Catalysts provide an alternative path of lower activation energy , so that more reactant molecules are able to reach the energy barrier (f) . Arrhenius Equation The Arrhenius Equation gives us the temperature dependence of of reaction rates . log10 k = log10 A - Ea/2.303 RT log10(k2/k1) = Ea/ 2.303 R T2-T1/T1T2 Collision Theory The basic requirement of collision theory is that the reactant molecules should come together and collide in order for the reaction to occur . Activation Energy The activation Energy (Ea) is the minimum kinetic energy required for a molecular collision to lead to reaction . Orientation If the molecules are not properly oriented , they do not react even at the activation energy . The molecules must be oriented relative to each other such that the groups reacting or bonds to be shifted are relatively close . Potential Energy Barrier Effect of Catalyst Category:Chemistry